Most people can hold their breath underwater for a few seconds, some for a few minutes. But a group of people can stay much longer under water - thanks to natural selection.
These special people are from the 'Bajau' tribe. Although they originated from Philippines, now they live in many other countries like Malaysia, Brunei, and Indonesia where they can thrive with their seaborne lifestyle. They use to free-dive to hunt for fish or search for natural resources. But these dives are not normal, they can stay underwater for breathtaking 15 minutes.
For this strange lifestyle, they have sometimes been called the "Sea Gypsies" or "Sea Nomads".
If a normal person dives underwater for few seconds, his heart rate will slow down, blood vessels will constrict, pupils will dilate, and spleen will contract. All these happen to save energy in low oxygen level. But these responses are different with 'Bajau' people. They have a mutation which gives them advantage in the deep.
You can technically live without your spleen, but while you have it, the organ helps support your immune system and recycle red blood cells. In marine mammals that spend most of their life underwater, spleens are disproportionately large. Melissa Llardo, a researcher from the Center for Geogenetics at the University of Copenhagen wanted to see if 'Bajau' people have the same characteristics. She said,
I wanted to first meet the community, and not just show up with scientific equipment and leave. On the second visit, I brought a portable ultrasound machine and spit collection kits. We went around to different homes, and we would take images of their spleens. If there's something going on at the genetic level, you should have a certain sized spleen. There we saw this hugely significant difference.
Other researchers also found a gene called PDE10A, which is thought to control a certain thyroid hormone which can influence spleen size.
Llardo theorizes that over time, natural selection would have helped the 'Bajau', who have lived in the region for a thousand years, develop the genetic advantage. In addition to understanding how the 'Bajau' became such good free divers, Llardo says the findings could help us understanding hypoxia in a better way.
However, the sea nomad lifestyle is increasingly under threat. They're considered marginalized groups that don't enjoy the same citizenship rights as their mainland counterparts. Increased industrial fishing is also making it harder for them to subsist on local stocks. As a result, many choose to leave the sea.
Without support for their way of life, Llardo worries that the 'Bajau' people may not be around for much longer.